RESUMEN
Integrative genomic and gene-expression analyses have identified amplified oncogenes in B-cell non-Hodgkin lymphoma (B-NHL), but the capability of such technologies to localize tumor suppressor genes within homozygous deletions remains unexplored. Array-based comparative genomic hybridization (CGH) and gene-expression microarray analysis of 48 cell lines derived from patients with different B-NHLs delineated 20 homozygous deletions at 7 chromosome areas, all of which contained tumor suppressor gene targets. Further investigation revealed that only a fraction of primary biopsies presented inactivation of these genes by point mutation or intragenic deletion, but instead some of them were frequently silenced by epigenetic mechanisms. Notably, the pattern of genetic and epigenetic inactivation differed among B-NHL subtypes. Thus, the P53-inducible PIG7/LITAF was silenced by homozygous deletion in primary mediastinal B-cell lymphoma and by promoter hypermethylation in germinal center lymphoma, the proapoptotic BIM gene presented homozygous deletion in mantle cell lymphoma and promoter hypermethylation in Burkitt lymphoma, the proapoptotic BH3-only NOXA was mutated and preferentially silenced in diffuse large B-cell lymphoma, and INK4c/P18 was silenced by biallelic mutation in mantle-cell lymphoma. Our microarray strategy has identified novel candidate tumor suppressor genes inactivated by genetic and epigenetic mechanisms that substantially vary among the B-NHL subtypes.
Asunto(s)
Proteínas Reguladoras de la Apoptosis/genética , Proteínas Portadoras/genética , Inhibidor p18 de las Quinasas Dependientes de la Ciclina/genética , Genes Supresores de Tumor , Proteínas de Homeodominio/genética , Linfoma de Células B/genética , Proteínas de la Membrana/genética , Proteínas Nucleares/genética , Proteínas Proto-Oncogénicas c-bcl-2/genética , Proteínas Proto-Oncogénicas/genética , Eliminación de Secuencia , Factores de Transcripción/genética , Proteínas de Transporte Vesicular/genética , Proteínas Adaptadoras Transductoras de Señales , Apoptosis/genética , Proteína 11 Similar a Bcl2 , Biopsia , Línea Celular Tumoral , Mapeo Cromosómico , Cromosomas Humanos/genética , Cromosomas Humanos/ultraestructura , Metilación de ADN , Análisis Mutacional de ADN , ADN de Neoplasias/genética , Epigénesis Genética , Dosificación de Gen , Regulación Neoplásica de la Expresión Génica , Silenciador del Gen , Homocigoto , Humanos , Linfoma de Células B/clasificación , Linfoma de Células B/inmunología , Linfoma de Células B/patología , Hibridación de Ácido Nucleico , Análisis de Secuencia por Matrices de Oligonucleótidos , Mutación Puntual , Regiones Promotoras Genéticas/genética , Proteínas de Unión al ARN , Nexinas de ClasificaciónRESUMEN
Epidemiological studies indicate the involvement of environmental factors in the etiology of breast cancer, but have not provided clear indications of the nature of the agents responsible. Several environmental carcinogens are known to induce mammary tumors in rodents, and the abundance of adipose tissue in the human breast suggests that the epithelial cells, from which breast tumors commonly arise, could be exposed to lipid-soluble carcinogens sequestered by the adipose tissue. In this report we review our studies in which we have examined human mammary lipid, obtained from elective reduction mammoplasties from healthy donors, and human milk from healthy mothers, for the presence of components with genotoxic activity in several in vitro assays. A significant proportion of lipid extracts induced mutations in bacteria and micronuclei in mammalian cells. They also caused DNA damage, detected as single-strand breaks in the alkaline single-cell gel electrophoresis (comet) assay, in both the MCL-5 cell line and in primary cultures of human mammary epithelial cells. Genotoxic activity was also found in a significant proportion of extracts of human breast milk. Viable cells recovered from milk samples showed evidence of DNA damage and were susceptible to comet formation by genotoxic agents in vitro. Genotoxic activity was found to be less prevalent in milk samples from countries of lower breast cancer incidence (the Far East) compared with that in samples from the UK. The agents responsible for the activity in milk appear to be moderately polar lipophilic compounds and of low molecular weight. Identification of these agents and their sources may hold clues to the origins of breast cancer.